P,N co-doped biomass carbon as a remarkable metal-free catalyst for solvent-free oxidation of benzyl alcohol with ambient air: The key promoting role of N co-doping

[Display omitted] •A P,N co-doped biomass carbon catalyst is prepared from the low-cost soybean flour.•Solvent-free oxidation of benzyl alcohol is achieved with the P,N-carbon catalyst.•The critical role of N co-doping is studied based on experiments and DFT calculation. Benzaldehyde is an important chemical intermediate, and its production via the oxidation of benzyl alcohol with O2 is highly pursued as an alternative for the existing industrial process to meet the demand of green chemistry. Most of the reported catalytic systems are dependent on the noble/toxic metal catalysts. Herein, a biomass carbon catalyst doped with P and N heteroatoms is prepared by calcinating the phosphoric acid-treated N-containing biomass of soybean flour in N2. In the absence of solvent or additive, the obtained P,N co-doped carbon catalyst exhibits aremarkablecatalyticactivity for oxidation of benzyl alcohol to benzaldehyde with air (99.4% yield, TOF = 62.1 × 10-4 mol BAD/(g catalyst × h reaction time)). The present turnover frequency surpasses all the previously reported ones of similar metal-free carbon catalysts for this reaction. The N co-doping facilitates the P doping into the carbon matrix, favors the formation the catalytic active species and has a remarkable electronic effect on them, which are identified via experiments and DFT calculations.